1. Field of the Invention
This invention relates to a device and a process for manipulation of a liquid which can flow from a first channel section to a second channel section and which can be temporarily stopped by means of a capillary stop before overflowing from the first channel section into the second channel section.
2. Description of Related Art
This invention relates to microfluidic systems and devices. The following text relates to devices in which capillary forces act and are decisive especially for operation.
In order to move liquids from one location to a next in a time controlled manner, so-called capillary stops are known, as disclosed, for example, in European Patent Application EP 1 441 131 A1 and corresponding U.S. Patent Application Publication 2004/0206408. In this connection, the liquid is temporarily stopped in a channel or in a wide chamber due to the sudden increase of capillary force. For example, the capillary stop can be formed by an especially trough-like control channel which runs transversely. When the control channel is flooded, for example, by a control liquid or by the liquid itself, the liquid can overcome the capillary stop. Accuracy in time and/or location is critical in this connection. When there is no tapering of the channel cross section in the area of the capillary stop, starting of the liquid defined in time over the entire channel cross section can only be achieved with difficulty or not at all. When the channel in the area of the capillary stop is tapered to obtain better time control or definition, the previously wider liquid front is narrowed and then often widened again, and as a result of diffusion processes, the local resolution of the study can be significantly adversely affected. Another problem consists in flooding the control channel quickly in an exactly controlled manner with respect to time.
European Patent Application EP 1 419 818 A1 and corresponding U.S. Patent Application Publication 2004/0096358 discloses stepwise controlling the transport of a liquid, especially temporarily stopping it, using so-called selective venting. This is done by stopping the air displacement in the channel to be flooded. Opening of the vent allows the liquid to continue to flow. The problem here is the hardware cost. Furthermore, the same problems arise with respect to time and/or local definition as in the aforementioned capillary stop with a control channel.
Moreover, external triggers, such as electrical and/or magnetic fields, surge waves or pressure waves are known to temporarily stop a liquid or to start liquid transport. In this connection, the hardware complexity, and thus, the costs are high.